Coating agent based on a hydroxyl group-containing polyacrylate resin and its use in processes for producing a multicoat paint system

An organic solvent based coating composition comprising

• (A) at least one hydroxyl-containing polyacrylate resin and
• (B) at least one isocyanate crosslinking agent, wherein the polyacrylate resin (A) is obtained by polymerizing, in an organic solvent or solvent mixture and in the presence of at least one polymerization initiator,
• (a1) an essentially carboxyl-free (meth)acrylic ester which is different from (a2), (a3), (a5), (a6) and (a7) and is copolymerizable with (a2), (a3), (a4), (a5), and (a6), or a mixture of such monomers,
• (a2) an ethylenically unsaturated monomer which carries at least one hydroxyl group per molecule and is essentially carboxyl-free, and is copolymerizable with (a1), (a3), (a4), (a5), (a6) and (a7) and is different from (a3), or a mixture of such monomers,
• (a3) at least one reaction product of acrylic acid and/or methacrylic acid with the glycidyl ester of an .alpha.-branched monocarboxylic acid having 5 to 18 carbon atoms per molecule or, instead of the reaction product, an equivalent quantity of acrylic and/or methacrylic acid which then, during or after the polymerization reaction, is reacted with the glycidyl ester of an .alpha.-branched monocarboxylic acid having 5 to 18 carbon atoms per molecule,
• (a4) optionally, an ethylenically unsaturated monomer which carries at least one carboxyl group per molecule and is copolymerizable with (a1), (a2), (a3), (a5), (a6) and (a7), or a mixture of such monomers,
• (a5) a polysiloxane macromonomer having a number-average molecular weight of from 1000 to 40,000 and on average from 0.5 to 2.5 ethylenically unsaturated double bonds per molecule or having on average from 0.5 to 2.5 epoxide groups per molecule, or a mixture of such monomers,
• (a6) an aromatic vinyl hydrocarbon, or a mixture of such monomers, and
• (a7) optionally, an essentially carboxyl-free, ethylenically unsaturated monomer which is copolymerizable with (a1), (a2), (a3), (a4), (a5) and (a6) and is different from (a1), (a2), (a3), (a5) and (a6), or a mixture of such monomers,
• wherein the nature and quantity of (a1), (a2), (a3), (a4), (a5), (a6) and (a7) are selected to provide a polyacrylate resin (A) having the desired OH number and acid number, and the quantity of component (a5) is less than 5% by weight, based on the overall weight of the monomers employed in preparing the polyacrylate resin (A), and wherein the polyacrylate resin (A) has an acid number of from 1 to 15.